The present invention relates to hydraulic pliers handy to carry and used for mounting and dismounting snap rings, especially of large nominal diameter, which, for the purpose of preventing the axial movement of bearings, collars and the like fitted on the shafts of various machines and instruments, are fitted in recessed peripheral grooves formed in the outer peripheral surface of said shafts or formed in the inner peripheral surface of shaft-engaging holes.
It is known in machinery fabrication that a snap ring is fixed in a projected manner on the peripheral surface of a shaft or of a shaft-engaging hole to thereby prevent the axial movement of a bearing, collar or the like mounted on the shaft. As otherwise called a C-shaped stop ring known in the art, such snap ring is usually opened at a part and is provided with sufficient elasticity to allow its opening and closing operation. For mounting and fixing such snap ring in position, it is temporarily expanded or contracted by utilizing its elasticity and forcefully fitted into a groove formed in the outer peripheral surface of a shaft or in the inner peripheral surface of a shaft-engaging hole.
That is, in the case of snap rings for use with shafts, since the inner diameter of the snap ring, adapted to fit the inner diameter of a recessed groove formed in the outer peripheral surface of a shaft, is, of course, smaller than the outer diameter of the shaft, when the ring is to be fitted in such groove it is required that the snap ring be temporarily and forcefully expanded and then be slid over the outer peripheral surface of the shaft until it reaches the recessed groove, whereat the hold upon the ring is released to restore its normal elasticity whereby the ring is tightly fitted in the groove. In the case of snap rings for use with holes, since the outer diameter of the ring, adapted to fit the inner diameter of a recessed groove formed in the inner peripheral surface of a shaft-engaging hole, is, of course, larger than the inner diameter of the hole, when the ring is to be fitted in such groove it is required that reversely, the snap ring be temporarily contracted and placed in the groove, whereat its elasticity is utilized to fix the ring in position. Thus, pliers (which may be referred to as ring setters) have been in wide use as a tool for practicing such operation. A conventional type of such pliers used particularly for large nominal diameter comprises a pair of opening and closing arms having working pins and pivotally connected together at a point in the form of a compass opend, a pair of operating handles respectively connected to said arms, one of said handles being integrally formed with a ratchet wheel, the other handle having a pawl attached thereto and normally elasticity urged into engagement with said ratchet wheel. With the working pins inserted in holes formed in the open ends of a snap ring, the user holds the handles with both hands to operate the handles so as to open and close the arms, so that with the degree of opening of the working pins being stepwise locked by the ratchet mechanism operatively associated with the opening and closing operation, the snap ring is forcefully deformed.
With such pliers, however, since the handles are long and must be held with both hands for operation, it is difficult to insert the working pins into the holes in the snap ring and in narrow places it is difficult to mount and dismount the snap ring with respect to said recessed peripheral groove. Further, since the deformation of the snap ring is attained solely by the user's force for opening and closing operation, much labor and time is expended in mounting or dismounting the snap ring. Further, since the pair of opening and closing arms are pivotally connected together at a point, the opening and closing motion of the working pins attained by the operation of the operating handles is an arcuate motion around the single pivot. Therefore, when the snap ring is being deformed, it is liable to warp and twist, while slippage is liable to occur between the holes in the ends of the snap ring and the working pins of the pliers. Thus, the operating force applied to the handles is not correctly and effectively transmitted to the snap ring.
On the other hand, unlike such manually operable opening and closing type, there is also known pneumatic pliers using compressed air force to open and close the working pins. With this type, although smooth operation and increased efficiency of operation can be attained, it is necessary to provide a compressed air source, such as a compressor, and piping, such as hoses, for introducing working air into the pliers, thus raising a problem that the pliers cannot be used in factories where there is no such accessory equipment. Another problem is that the presence of the piping puts limitations on working environment.